1. Field of the Invention
This invention relates to jet drilling drain holes from well bores, primarily in oil and gas wells.
2. Description of Related Art
Oil and gas wells are usually drilled vertically and cased with steel pipe. Typical casing pipes are from 4.5 to 8 inches in diameter. In a typical short-radius jet drilling technique, a flexible tubing or hose attached to the bottom of small rigid tubing (work string) turns 90 degrees within a channel in a diverter attached to a larger (production) tubing inside the casing. Fluid is pumped through the work string, flexible tubing and a bit on the flexible tubing to drill drain holes that may extend 15 to 100 ft. or more from the casing into the rock formation. The drain holes allow more contact area with the rock formation, increasing the flow capacity of the well. Buckman (U.S. Pat. No. 6,668,948), Landers (U.S. Pat. No. 5,413,184) and others have developed short-radius drilling systems that have a radius of 4 inches or less, in which a jet bit (nozzle) and hose pass down through a tubing string in a vertical well to a diverter, which contains a path to deviate the jet bit and flexible hose to enable drilling deviated or horizontal laterals or drain holes in oil and gas wells.
There are limiting factors that can prevent a flexible hose from passing through a tight 90-degree turn in a 4-inch radius. Like coiled tubing, a flexible hose can sinusoidally, helically buckle, causing extra friction or drag. Reduction of friction between a flexible hose and surrounding pipe can allow more force to be applied at a bit. Excess friction may lead to “lockup.” When lockup occurs, no matter how much force is applied the tubing can no longer move. If excessive force is continually applied from above in a larger tubular (well tubing) having sufficient diameter, the work string and the flex hose can “pass by itself,” meaning that the flexible tubing turns enough to pass alongside the work string and inside the larger (production) tubing. In this condition, an observation at the surface of the work string rapidly going down the production tubing creates the illusion of jet drilling of the formation while the jet bit is not moving.
Another problem in conventional short-radius drilling is that a jet bit may “catch” inside threaded connections of jointed production tubing. If this occurs during the deployment of the jet bit and flex hose downhole, it has been observed that it is near impossible to complete the trip of the bit to the diverter.
A further problem is knowing when the jet bit is at the diverter and then in a position to be engaged at the formation. Without simple and precise knowledge of formation engagement one can falsely claim the drilling of a formation.
Method and apparatus are needed to eliminate the jet bit catching on tubing connections as it is inserted through the tubing down the well. A signal or indication at the surface is also needed when the jet bit encounters the diverter and the formation, and a technique to transmit greater axial force to the jet bit as it passes through the diverter and jet drills is needed.